Move 'invalid super qualifier' error to new error format.

As part of https://github.com/lampepfl/dotty/issues/1589, use the
new error message for static super references where the qualifier
isn't a parent of the class.

Tested:
  Added unit test.

2 files changed, 18 insertions, 0 deletions

diff --git a/compiler/src/dotty/tools/dotc/reporting/diagnostic/ErrorMessageID.java b/compiler/src/dotty/tools/dotc/reporting/diagnostic/ErrorMessageID.java
index 7b56c8ed4..6ea168b99 100644
--- a/compiler/src/dotty/tools/dotc/reporting/diagnostic/ErrorMessageID.java
+++ b/compiler/src/dotty/tools/dotc/reporting/diagnostic/ErrorMessageID.java
@@ -55,6 +55,7 @@ public enum ErrorMessageID {
     RecursiveValueNeedsResultTypeID,
     CyclicReferenceInvolvingID,
     CyclicReferenceInvolvingImplicitID,
+    SuperQualMustBeParentID,
     ;
 
     public int errorNumber() {
diff --git a/compiler/src/dotty/tools/dotc/reporting/diagnostic/messages.scala b/compiler/src/dotty/tools/dotc/reporting/diagnostic/messages.scala
index 4c53fa496..6fa056646 100644
--- a/compiler/src/dotty/tools/dotc/reporting/diagnostic/messages.scala
+++ b/compiler/src/dotty/tools/dotc/reporting/diagnostic/messages.scala
@@ -1192,4 +1192,21 @@ object messages {
            |""".stripMargin
   }
 
+  case class SuperQualMustBeParent(qual: untpd.Ident, cls: Symbols.ClassSymbol)(implicit ctx: Context)
+  extends Message(SuperQualMustBeParentID) {
+
+    val msg = hl"""|$qual does not name a parent of $cls"""
+
+    val kind = "Reference"
+
+    private val parents: Seq[String] = (cls.info.parents map (_.name.show)).sorted
+
+    val explanation =
+      hl"""|When a qualifier ${"T"} is used in a ${"super"} prefix of the form ${"C.super[T]"},
+           |${"T"} must be a parent type of ${"C"}.
+           |
+           |In this case, the parents of $cls are:
+           |${parents.mkString("  - ", "\n  - ", "")}
+           |""".stripMargin
+  }
 }